Morphology and general characteristics of viruses active against cowpea Rhizobium CB756 and 32H1.

Two newly isolated viruses, RS1 and RS2, infective on two strains of cowpea Rhizobium capable of N2-fixation in vitro, were characterized. RS1 parasitizes CB756 but RS2 infects both 32H1 and CB756. RS1 has an isometric, polyhedral head and a long contractile tail, while RS2 has an oblate, polyhedral head and a long flexible non-contractile tail; RS1 is considerably larger than RS2. The phages were relatively stable between pH 5 and 9 (1 hour incubation). RS1 appeared to be more thermal sensitive and exhibited one component inactivation, while RS2 showed two component inactivation at 58, 60 and 62 degrees C. RS1 had a slower adsorption rate (3.3 X 10(-10) ml minutes-1) than RS2 (1.2 X 10(-9) ml minutes-1, on 32H1). The latent period of RS1 and RS2 was 180 and 225 minutes, and the burst size was 15 and 9 particles/cell, respectively.